Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $209.51   11.689%   $233.9996   $234.00   $234.00   $234.00  
  Purchase #2 $136.95   9.569%   $150.0547   $150.05   $150.05   $150.10  
  Purchase #3 $222.60   8.535%   $241.5989   $241.60   $241.60   $241.60  
  Purchase #4 $59.50   7.797%   $64.1392   $64.14   $64.15   $64.10  
  Purchase #5 $11.99   8.757%   $13.04   $13.04   $13.05   $13.00  
  Purchase #6 $51.41   3.467%   $53.1924   $53.19   $53.20   $53.20  
  Purchase #7 $91.97   8.570%   $99.8518   $99.85   $99.85   $99.90  
  7 purchase totals = $783.93       $855.8766   $855.87   $855.90   $855.90